1. Field of the Invention
This invention relates to a liquid, pasty, thixotropic, semisolid or solid hardenable substance which is based on monomeric, oligomeric and/or polymeric compounds and one or more components that promote hardening, whereby at least the monomeric, oligomeric or polymeric compounds and/or the components promoting hardening are enclosed in a reaction-preventing protective casing containing a rupturing agent for the protective casing. The composition may contain other conventional additions.
More particularly, this invention relates to one-component substances in which at least one of the reaction partners, reaction initiators, reaction accelerators and/or adducts or additives are temporarily inactivated by protective casings.
One-component systems according to the present invention are intended to mean substances of mixtures of liquid, pasty, thixotropic, semisolid and/or solid reactive materials. They may, in addition, contain inert filling materials, pigments, dyes, plasticizers, bitumens, tars, pitches, resins and/or solvents. In addition, the invention relates to the production of such substances, the hardening of same and their application.
2. Description of The Prior Art
In practice, the advantages and the merits of two and more component substances based on an inorganic, organometallic and/or organic base are well known. However, these two and more component systems have several marked disadvantages due to which their application in many fields of engineering and trade is made impossible. Such negative features include the fact that they require intricate and/or unduly expensive two or more component dosing and mixing appliances, critical mixing ratios entailing the danger of errors in mixing, short pot and processing times, exothermic reactions when handling large batches, physiological doubts in regard to many reactive substances, etc.
Many efforts have been made to create one-pot or one-component systems that are free from these negative features. Thus, technical progress has been achieved by means of one-component systems reactivated by atmospheric moisture, (e.g., substances based on silicon rubbers, polyurethanes and polysulfides). However, for a number of reasons many two and more component systems cannot be reformulated to adapt them to moisture hardening or for processing in industrial practice. Furthermore, among other things, moisture hardening systems have the disadvantage that the hardening rates are very low (several days) and depend on the layer thickness and/or the relative humidity of the ambient air. In addition, the production of such moisture hardening systems calls for special care and expensive mixing appliances with vacuum equipment.
For this reason, attempts have been made in recent times to avoid the negative features of such systems by coating at least one of the two reaction partners with protective casings. For the jacketing or encasing of such liquid droplets and/or solid particles with chemically inert wall materials there are a number of known and preferred encapsulating techniques and particularly preferred is microencapsulation. For simplicity, reference hereinafter shall be made to microencapsulates and microencapsulated materials, even where, in general, protective casings are intended.
To obtain a temporarily effective inactivation of the substances, the protective casings must fulfill a multiplicity of requirements, as a result of which new critical parameters are established by the use of microencapsulated materials for this purpose. Thus, the protective casings or wall materials must be chemically inert to the internal and external phase, impervious to diffusion, unbreakable, elastic and flexible and possess stability to temperature changes. Furthermore, varying dipole moments must not result in an exchange of materials in the internal and external phase.
To ensure that the protective casings and wall materials possess these and other desired properties, various forms of aftertreatment are necessary. In many instances, specific shrinking and hardening methods are insufficient and it is necessary to draw secondary walls over the protective casings. However, this does result in protective casings that are impervious to diffusion, unbreakable and stabile to storage, which results in the smaller capsules being less destroyable by strongly increased pressures and/or shearing forces. Furthermore, the wall materials on small capsules are also stronger and more stabile, which is the reason for their decreased destructibility.
Another disadvantage prevails in the incorporation of microencapsulated materials into systems with high viscosity, thixotropy and/or a high degree of filling material, particularly with granular and acutely tapered filling materials. The high shearing forces necessary for the mixing process are, in many instances, so strong that, as a result, the protective casings are at least partially cracked and the reactive materials that issue forth initiate undesirable reactions.
Also, reactive substances that contain microencapsulated materials and are intended for precoating surfaces that are to be joined or sealed, have the further disadvantage that the predetermined wall thicknesses of the microencapsulated materials cannot be adapted to the changing tolerances and are movable within the hollow spaces of the joint. For example, if the hollow space of a joint is not completely filled with such a material, then, at least at the border surfaces, a full-surface binding effect will not be obtained, resulting in a loss of binding strength or leakiness. A further negative feature is that capsule rupture takes place only at the contact points so that only a partial hardening takes place. In such cases where the tolerances are smaller than the preselected layer thicknesses, the substance is deflected away from the precoated surfaces, so that, again, hollow unfilled joint spaces result. For example, in metallic plug-in connections, such deficiencies may result in defects due to the fact that pressure will not be applied and the substance will not react and, consequently the specified hardening is not achieved.
In order to avoid the negative features in regard to plug-in and joint connections, it has been suggested to scatter or strew friction bodies composed of a metal oxide into the applied, but still wet coating substance as rupturing agents for the protective casing. Beside the extra processing manipulations involved in the strewing-in and the subsequent elimination of superfluous friction bodies required where partial capsule breaking may already have occurred, an additional negative feature crops up due to the inhomogenous composition of the adhesive substance.
It has also been attempted to equip diverse substrate and material surfaces with dry, nonadhesive, adhesive layers having good storage stability containing microencapsulated solvents in which the solvents become reactive when subjected to pressure and/or impact. Practical use, however, has showed that the pressure and impact forces are not adequate to rupture the protective casing, particularly on relatively small capsules so that the outflowing solvent would reactivate the adhesive substance by swelling and dissolving.
The causes of the problems that crop up in regard to liquid, pasty, thioxotropic and semisolid substances for spackling, filling, stamping and coating purposes which contain microencapsulated substances are to be found in the lack of frictional effect and the minor mechanical forces involved in spackling and stamping, whereas substances with coarse-grained fillers have, to date, not been producible.
In German patent application DT AS 2 200 163, dry mortar and spackling compounds based on calcined gypsum are described which contain microencapsulated auxiliary materials. An inherent disadvantage of these substances is, among other things, that despite long swelling and dissolving periods and/or intense mechanical stress, only partial, and often only minor capsule destruction is obtained. Since the degree of capsule destruction, under the given conditions, is not a controllable or regulatable factor, the properties of the material can vary, e.g., between batches which have been produced under identical conditions. This is particularly the case with auxiliary materials where very small added quantities exert a strong modification effect.
The attempt has also been made in the field of reinforced plastic material, and especially glass fibre reinforced polyester (GFK), to obtain reactivatable single component systems that contain microencapsulated reaction partners. The attempted solution of this problem failed because a homogeneous distribution coefficient for the microencapsulated reaction initiators and a high capsule rupturing quota (at least 90 and more %) could not be achieved. The poor capsule rupturing quota is due to pressures that are too low and or too brief.
The above described disadvantageous and other negative features of the known one-component systems that contain microencapsulated reactive substances may be summarized in the following two marked negative characteristics:
1) due to high friction in the mixing process, it was not possible to produce any substances with high viscosity and/or thixotropic values, especially in the presence of angular edged and/or acute sharply tapered filler materials; PA0 2) the pressure, shearing, rotational and/or torsional forces were not sufficient to effect an optimal capsule rupture.